An organic electroluminescence (EL) device is a promising solid-state emitting type inexpensive and large full-color display device, and has been extensively developed. In general, an organic EL device includes an emitting layer and a pair of opposing electrodes holding the emitting layer therebetween. Emission is a phenomenon in which when an electric field is applied between the both electrodes, electrons are injected from the cathode and holes are injected from the anode. The electrons recombine with the holes in the emitting layer to produce an excited state, and energy is emitted as light when the excited state returns to the ground state.
Conventional organic EL devices have a higher driving voltage than that of an inorganic light-emitting diode. The luminance or luminous efficiency thereof is also low, and their properties tend to deteriorate significantly. For these reasons, conventional organic EL devices have not been put in a practical use. Although recent organic EL devices have been improved gradually, further improvement in luminous efficiency, prolongation in lifetime or the like has been demanded.
In order to attain a high luminous efficiency and a long life, some organic EL devices and some materials for an organic EL device have been proposed (Patent Documents 1 to 4). However, further improvement has been demanded.